Hi,

 

I have had a look through the archives but not really finding the answer I'm looking for.

 

Running a stock setup, with 18" rims (staggered so 9" on the rear and 8" on the front), please can someone tell me what tyre sizes I'm looking at?

 

I'm thinking 265/35/18 on the rear, is this as wide as I can go without rubbing? On the front I'm guessing 235/35/18?

 

Does it need to be 35 to keep the original circumference the same (would a 40 matter for example), how crucial is this? I don't want to be going 35mph and showing 30mpg on the speedo etc.

 

I don't want to stretch the tyres or anything like that, just a normal setup.

 

Cheers :)

Those are the tyres i have on my 18s :thumbup1:

The small number. 35,40 etc are a percentage so a 265/35 is equalish to a 225/40 in terms of rolling diameter. There are calculators available if you search to work these things out.

I have 225/40/18 on the front and 265/35/18 on the rear. Is that not right ?

 

is there some flex on the size as mastercookieman says ? Or do I have the wrong set up ?

 

I have not checked the speedo against my sat nav as speedo is in KPH. Will report back on when I take it for a spin.

 

 

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You need to keep the rolling circumference the same (or as close as possible) front to rear.....

 

.....So if you have 265/35/18 on the rear, then you need 235/40/18 on the front.

Top man Stephen.

 

 

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The small number. 35,40 etc are a percentage so a 265/35 is equalish to a 225/40 in terms of rolling diameter. There are calculators available if you search to work these things out.

 

Bang on....:cool:

 

265mm @ 35% = 92.75mm so x2 (top and bottom profile)/25.4+18 = 25.3 inch diameter

235mm @ 40% = 94.00mm so x2/25.4+18 = 25.4 inch diameter = close enough!

Cool... This forum is educational as well !!Thanks for the maths.

 

 

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Cool... This forum is educational as well !!Thanks for the maths.

 

 

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LOL - you're welcome mate.....

 

......And what else would you expect from an accountant....:biggrin:

I don't have that!

I have this! As already said?

265/35 rear

225/40 front

Ok, thanks everyone, I get the 265/30, but how do we end up with 40 on the front? I understand it's to keep it as close to the original as possible, so were the original 16" tyres also different tyre heights? I guess they must have been.

 

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The tyre heights won't be different sizes, that's the point. The number that dictates the sidewall height isn't a direct unit measurement (like the width which is in mm), it is a percentage of that width in mm.

 

As shown in Richard's calculations, 35% of 265mm is an equivalent dimension to 40% of 235mm. If you chose a 235/35 tyre for the front, then your tyres will have different heights.

 

Tyre sizes are a bit like JaiKai's garage/workshop plans, they contain a mixture of different unit measurements!

I have 225/45 front and 265/35 rear. Will be going with 225/40 fronts when I change as the 45 is a bit on the big side. Max 5% difference is the law around here

 

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Most tyre manufacturers publish the full specifications including the overall diameter for each of the tyres they make.

The overall diameter is a function of the tyre size, width and aspect ratio. So for example, if you take a look at the

specifications published by Toyo tyres for thier Proxes T1 Sport you can see the dimensions we are interested in for

each tyre:

 

http://www.toyo.co.uk/tire/pattern/proxes-t1-sport (click on "Specifications" tab to get table)

 

The idea when selecting tyres is to keep the F&R tyres overall diameters as close as possible and in turn close to the

original OEM tyres overall diameter.

 

Toyo also publish the approved rim width for each tyre size with the optimum size highlighted.

Joely P...that tyre picture with annotation is really useful with the maths calcs [emoji106]

 

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